U.S. patent number 5,279,157 [Application Number 07/923,524] was granted by the patent office on 1994-01-18 for liquid level monitor.
This patent grant is currently assigned to Casco Products Corporation. Invention is credited to Ali El-Haj, Kenneth J. Kelemen, Donald J. Mattis, Lisa Toth.
United States Patent |
5,279,157 |
Mattis , et al. |
January 18, 1994 |
Liquid level monitor
Abstract
A liquid level monitor for sensing the level of liquid in a tank
or vessel, typically an automobile radiator, employing a probe with
a light emitting diode and phototransistor mounted inside an
enclosure, the enclosure having a transparent lens through which
light can pass, and the lens having a prism configuration which
diffuses or alters stray light which occurs by reflection off an
interior core wall of the vessel and prevents the diffused or
dispersed light from rendering the phototransistor conductive and
possibly leading to a false indication or reading of liquid level.
The light emitting diode is electrically excited with a
high-intensity, short duration pulse, which improves the
sensitivity of the monitor.
Inventors: |
Mattis; Donald J. (Norwalk,
CT), El-Haj; Ali (Trumbull, CT), Toth; Lisa
(Huntington, CT), Kelemen; Kenneth J. (Fairfield, CT) |
Assignee: |
Casco Products Corporation
(Bridgeport, CT)
|
Family
ID: |
25448831 |
Appl.
No.: |
07/923,524 |
Filed: |
August 3, 1992 |
Current U.S.
Class: |
73/290R; 250/557;
250/903 |
Current CPC
Class: |
G01F
23/2925 (20130101); Y10S 250/903 (20130101) |
Current International
Class: |
G01F
23/292 (20060101); G01F 23/284 (20060101); G01F
023/22 () |
Field of
Search: |
;73/29R,293 ;250/577,903
;356/135,136,137 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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65798 |
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Dec 1982 |
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EP |
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2251210 |
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Oct 1972 |
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DE |
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2726082 |
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Dec 1978 |
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DE |
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2920199 |
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Dec 1979 |
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DE |
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2849066 |
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May 1980 |
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DE |
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3021374 |
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Dec 1981 |
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DE |
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3247198 |
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Jul 1984 |
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DE |
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126461 |
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Oct 1975 |
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JP |
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119260 |
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Oct 1976 |
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JP |
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14803 |
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Aug 1983 |
|
JP |
|
214715 |
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Dec 1984 |
|
JP |
|
89163 |
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Dec 1987 |
|
JP |
|
8903978 |
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May 1989 |
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WO |
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615995 |
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Feb 1980 |
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CH |
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412803 |
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Jul 1934 |
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GB |
|
87/01801 |
|
Mar 1987 |
|
WO |
|
Other References
Aeroquip Product Information and Application News. TIN-2, Summer
1986, "Tedeco Levelmaster Electro-Optic Liquid Level Sensor", 2
pages. .
Aeroquip Tedeco Division Bulletin TDB L250, "Tedeco Levelmaster 250
Series", 1987, 2 pages..
|
Primary Examiner: Will; Thomas B.
Assistant Examiner: Bennett; G. Bradley
Attorney, Agent or Firm: Bittman; Mitchell D. Lehmann; H.
Gibner
Claims
What is claimed is:
1. A liquid level monitor, comprising in combination:
a) a housing having a lens in one wall, said wall and lens being
adapted for submersion in liquid whose level is to be
monitored,
b) a light emitting diode and a photo-responsive device in said
housing, both facing in a common direction toward said lens,
and
c) light-passing and altering means located on the exterior of said
lens, said means being cooperable with said lens for attenuating
predetermined portions of reflected stray light which have
originated at the light emitting diode and which have passed
outwardly through the lens, and which have been externally
reflected onto the exterior of the lens from a point which is
spaced from the lens and which is exterior to the said housing.
2. The invention as set forth in claim 1, wherein:
a) said light-passing and altering means comprises prism
configurations on the outer surface of said lens.
3. The invention as set forth in claim 2, wherein said prism
configurations comprise a series of substantially parallel
ribs.
4. The invention as set forth in claim 2, wherein said prism
configurations comprise a series of pyramids, spaced side by
side.
5. The invention as set forth in claim 3, wherein the ribs have
troughs between them, and the angle between the walls of each
trough is between 72.degree. and 90.degree..
6. The invention as set forth in claim 3, wherein the ribs have
troughs between them, and the angle between the walls of each
trough is on the order of 84.degree..
7. The invention as set forth in claim 1, wherein the lens has a
conical exterior surface configuration, and the light-passing and
altering means is disposed in the conical surface of the lens.
8. The invention as set forth in claim 7, wherein the lens has a
center recess at its inner side opposite to the conical surface
thereof.
9. The invention as set forth in claim 1, and further including a
reflecting surface disposed opposite the lens, and spaced a
distance therefrom.
10. The invention as set forth in claim 9, wherein said reflecting
surface comprises a core wall of an automotive radiator.
11. The invention as set forth in claim 10, wherein said liquid
comprises a translucent radiator coolant.
12. The invention as set, forth in claim 1, wherein:
a) said light-passing and altering means comprises multiple
pyramids, spaced side by side, on the outer surface of said
lens.
13. The invention as set forth in claim 1, wherein:
a) said light-passing and altering means comprises multiple prisms,
formed by a set of substantially parallel ridges and grooves, and a
second set of substantially parallel ridges and grooves, said
second set being substantially perpendicular to the first-mentioned
set of ridges and grooves, respectively.
14. The invention as set forth in claim 1, wherein:
a) said light-passing and altering means comprises a peripheral
conical surface, and a series of circular ridges within said
conical surface, said ridges being substantially concentric with
one another, and being separated from one another by circular
grooves.
15. The invention as set forth in claim 14, wherein the walls of
the circular grooves have a matte finish.
16. The invention as set forth in claim 1, and further
including:
a) an automotive vehicle radiator having a heat-exchanger core and
a jacketing wall exterior to said core in closely spaced relation
thereto,
b) said core having a reflective tube sheet defining with said
jacketing wall a coolant reservoir area,
c) said housing being mounted on said jacketing wall and with its
lens facing said tube sheet.
17. A liquid level monitor for a tank or vessel, said tank having
an aperture in a side wall, and containing a generally translucent
liquid, and said tank having a core with a light-reflective
interval wall surface, the monitor comprising in combination:
a) a liquid level indicator probe comprising a housing carried in
the aperture of said tank side wall, said indicator probe having
walls and a lens in one of its walls, said lens being adapted for
submersion in the liquid in the tank,
b) a light emitting diode and a photo-responsive device in said
probe housing, both facing in a common direction toward said lens,
and
c) light-altering means which is cooperable with said lens, for
attenuating predetermined portions of light which originate from
the light emitting diode, pass through the translucent liquid,
impinge on said light-reflective internal wall surface of the core
and are reflected back therefrom, through the lens and to the
photo-responsive device, and which could otherwise cause erroneous
readings of the liquid level.
18. A liquid level monitor for a tank or vessel, said tank having
an aperture in a side wall, and containing a generally translucent
liquid, said tank having an internal core with a light-reflective
internal wall surface, the monitor comprising in combination:
a) a liquid level indicator probe comprising a housing carried in
the aperture of said tank side wall, said indicator probe having
walls and a lens in one of its walls, said lens being adapted for
submersion in the liquid in the tank,
b) a light emitting diode and a photo-responsive device in said
probe housing, both facing in a common direction toward said lens,
and
c) means on said lens, for discriminating between light that is
generated by the light emitting diode and internally reflected by
the lens to arrive at the photo-responsive device, and stray light
that is generated by the light emitting diode, passes outwardly
through the lens and translucent liquid, impinges on and is
reflected from the light-reflective internal wall of the tank to
re-enter the lens and strike the photo-responsive device, thereby
to prevent an erroneous low reading of liquid level due to such
stray light.
19. An automotive radiator and coolant level monitor therefor,
comprising in combination:
a) a radiator tank having an apertured side wall, and containing a
generally translucent coolant liquid,
b) a light-reflective internal wall surface disposed in said
radiator tank,
c) a coolant level indicator probe comprising a housing carried in
the aperture of said radiator tank side wall, said indicator probe
having walls and a lens in one of its walls, said lens being
adapted for submersion in the coolant liquid in the tank,
d) a light emitting diode and a photo-responsive device in said
probe housing, both facing in a common direction toward said lens,
and
e) light-altering means which is cooperable with said lens, for
attenuating predetermined portions of light which originate from
the light emitting diode, pass through the coolant, impinge on said
light-reflective internal wall surface of the radiator tank and are
reflected back therefrom, through the lens and to the
photo-responsive device, and which could otherwise cause erroneous
readings of the coolant level.
20. An automotive radiator and coolant level monitor therefor,
comprising in combination:
a) a radiator tank having an apertured side wall, and containing a
generally translucent coolant liquid,
b) a light-reflective internal wall disposed in said radiator
tank,
c) a coolant level indicator probe comprising a housing carried in
the aperture of said radiator tank side wall, said indicator probe
having walls and a lens in one of its walls, said lens being
adapted for submersion in the coolant liquid in the tank,
d) a light emitting diode and a photo-responsive device in said
probe housing, both facing in a common direction toward said lens,
and
e) means on said lens, for discriminating between light that is
generated by the light emitting diode and internally refracted by
the lens to the photo-responsive device, and stray light that is
generated by the light emitting diode, passes outwardly through the
lens and coolant and is reflected from the light-reflective
internal wall of the radiator tank, and which thereafter re-enters
the lens as a dispersed beam and strikes the photo-responsive
device, thereby to prevent an erroneous reading of coolant level
due to such stray light.
Description
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSORED
RESEARCH AND DEVELOPMENT.
Research and development of the present invention and application
have not been Federally-sponsored, and no rights are given under
any Federal program.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to liquid level monitors, and more
particularly to improvements in the monitoring apparati disclosed
and claimed in U.S. Pat. Nos. 4,840,137 and 4,859,987. The first of
these patents issued Jun. 20, 1989, is entitled LIQUID LEVEL
GAUGING APPARATUS, and has common ownership with the present
application. U.S. Pat. No. 4,859,987 issued Aug. 22, 1989, is
entitled APPARATUS AND METHOD FOR MONITORING LIQUID LEVELS and also
has common ownership with the present application. Accordingly, the
entire disclosures of U.S. Pat. Nos. 4,840,137 and 4,859,987 are
specifically incorporated by reference, into the present
application.
2. Description of the Related Art Including Information Disclosed
Under 37 CFR 1.97 and 37 CFR 1.98
In U.S. Pat. No. 4,840,137 above identified, the disclosed monitor
employs a photocell and light emitting diode housed in a cup-like
prism which has at its outer end a generally conical surface
indicated by the reference numeral 102. This device was intended to
be installed in the wall of the oil pan of an automotive vehicle.
Its operation, as indicated in column 12, lines 31-36, is as
follows: When the oil level in the pan is below a certain point on
the cone 102, light from the light emitting diode is reflected
internally of the cone and impinges upon the phototransistor,
causing it to conduct. The resultant condition is employed to drive
circuitry that provides the desired warning, namely to the effect
that a low oil level exists in the pan.
However, when the oil level is normal, the cone 102 is covered and
light impinging on the oil-cone interface is not sufficient,
following reflection within the prism, to trigger the
phototransistor.
While the disclosed arrangement has successfully been in use
commercially for several years, attempts were made to extend the
application of the apparatus to other equipment involving
monitoring the level of various other liquids of the
automobile.
The present invention constitutes an improvement by which the level
of liquids other than crankcase oil can be monitored, as for
example the coolant in the radiator of an automobile engine, heat
exchanger, or other equipment.
An effort was made to adapt the monitor device of U.S. Pat. No.
4,840,137 for use with an automobile radiator. However, it was
found that special conditions existed in radiators due to the heat
exchanger core being closely jacketed at the reservoir area, which
resulted in extremely confined spaces whereby under conditions of
normal liquid levels and with liquids of a type which are generally
more translucent than motor oil, substantial undesirable amounts of
light were passing out through the surface of the cone 102, through
the radiator liquid, striking a closely-located opposite internal
surface of the radiator at the reservoir area, and then being
reflected back to the cone in a manner to register on the
phototransistor as an erroneous low level indication.
The reflective surface of the reservoir area in this case was
within a fraction of an inch of the cone, typically less than
one-quarter of an inch.
SUMMARY OF THE INVENTION
The problem set forth above in connection with the prior patented
monitor sensor is obviated by the present invention, which has for
one object the provision of a novel and improved gauge or monitor
module for a liquid-containing vessel characterized by very
confined internal spaces, which eliminates the undesired effect of
stray light reflections from the internal surfaces in the vessel
that lead to erroneous liquid level readings.
Yet another object of the invention is to provide an improved
monitor or gauge as above set forth, which is not only simple in
construction and reliable in operation but also economical to
manufacture and produce, being largely fabricated from molded
plastic components that interfit with one another.
Still another object of the invention is to provide an improved
monitor gauge in accordance with the foregoing, which is rugged and
resistant to damage resulting from impact, or from extremes of heat
and cold.
A still further object of the invention is to provide an improved
monitor or gauge as above characterized, which is resistant to
inadvertent leaks, and capable of operation with hot, pressurized
liquids of the type normally encountered in the radiator of an
internal combustion engine.
In accomplishing the above objects the invention provides a monitor
module, comprising a housing having a lens in one wall, the wall
and lens being adapted for submersion in liquid whose level is to
be monitored, a unique light emitting diode and a photo-responsive
device in the housing, both facing in a common direction toward the
lens, and a light-altering means which is cooperable with the lens,
for attenuating predetermined portions of light originating from
the light emitting diode and which might be externally reflected
against the exterior of the lens from a point which is exterior to
the the module's housing.
The light-altering means is sufficient to block the effects of
stray light which is reflected from a closely juxtaposed inner
surface such as a heat-exchanger core structure in the radiator or
vessel and returned to the lens, while still not interfering with
the normal functioning of the monitor in distinguishing between its
lens being immersed in air or in the liquid being monitored.
In a preferred embodiment of the invention, the light emitting
diode is driven with a high-intensity, short-duration electrical
pulse which produces a momentary level of brightness that
substantially exceeds the steady state light output normally
obtainable with steady d. c. excitation, and the lens' outer
surface is provided with a ribbed or textured configuration which
has the desired effect of altering or diffusing undesired reflected
light originally passing outwardly through the lens surface and
entering the space beyond the lens, and which is then reflected off
of an internal surface or a wall of the vessel with which the
monitor module is being employed.
Other features and advantages will hereinafter appear.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, illustrating several embodiments of the
invention:
FIG. 1 is a side view, partly in elevation and partly in axial
section, of the improved liquid level monitor module of the
invention.
FIG. 2 is a view like FIG. 1, taken at 90.degree. to the showing of
FIG. 1.
FIG. 3 is a fragmentary left end elevation of the monitor module of
FIGS. 1 and 2.
FIG. 4 is a fragmentary right end elevation of the monitor module
of FIGS. 1-3.
FIG. 5 is a fragmentary axial section, greatly enlarged, similar to
FIG. 2 but rotated 180.degree. therefrom, and in addition showing
the monitor module mounted in the wall of a liquid-containing
vessel such as an automotive vehicle's radiator, at the
water-reservoir area thereof.
FIG. 6 is a fragmentary right end elevation, greatly enlarged, of
the module of FIG. 5.
FIG. 7 is a fragmentary right end elevation, greatly enlarged,
showing a modified lens, constituting a second embodiment of the
invention.
FIG. 8 is a diagrammatic showing of the electrical circuit
employing the light emitting diode and photo-responsive device as
embodied in the monitor of the present invention.
FIG. 9 is a fragmentary axial section of a further modified lens,
constituting another embodiment of the invention.
FIG. 10 is a right end elevation of the lens of FIG. 9, and
FIG. 11 is a diagram of the module mounted on a car radiator,
specifically on the wall of the water reservoir or area and close
to the core wall thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1, 2, 5 and 11, the liquid monitor of the
present invention is in the form of a probe or module 10 which is
adapted to be mounted in a vessel or radiator 11 (FIG. 5) by means
of a tubular fitting 12 in the jacketing wall 14 of the radiator at
the water reservoir area. The jacket or water reservoir wall 14 has
an opening 16 which communicates with the interior of the fitting
12. To the right of the wall 14 is the radiator core wall 18
depicted in solid outline, this being the support for the core or
heat-exchanger assemblage 19 (FIG. 11) which is disposed within the
radiator 11. Depending on the particular make of the radiator, the
wall 18 can be even closer, as for example in the position shown in
dotted outline 18'.
The fitting 12 can be a separate piece, as shown, suitably attached
as by welding to the radiator wall 14, or else it can be formed
integrally with the wall, if desired, depending on the particular
construction of the radiator.
FIG. 11 diagrammatically illustrates the radiator jacketing walls
14 and 15, and radiator core walls or heat-exchanger tube sheets 13
and 18, along with the connecting tubes constituting the core
assemblage 19. Between the walls 14 and 18 there is a coolant
reservoir area 14', and between the walls 13 and 15 there is a
similar coolant reservoir area 15'. The radiator coolant is
indicated by the numeral 98 in FIG. 11.
The module 10 comprises a cup shaped enclosure 20 with an annular
side wall 22 and a transverse end wall 24. The cup shaped enclosure
20 is telescopically received in a module housing designated 26,
which has a terminal block 30 and an oval-shaped rigid skirt 32
defining an oval recess 34. The open end of the cup shaped
enclosure 20 has an annular groove 36 surrounded by a projecting
skirt 38, and the module housing 26 has a similar mating structure
comprising an annular wall 40 which is received in the groove 36 of
the cup-shaped enclosure 20. An O-ring 42 is disposed between the
enclosure 20 and housing 26 and constitutes a compressible seat
when the enclosure 20 and housing 26 are assembled.
On the outer surface of the cup shaped enclosure 20 are multiple
retainer lugs 44, one such lug being shown in FIG. 1. The housing
26 also has multiple recesses 46, one of which is shown in FIG. 1,
the recesses 46 being adapted to receive the lugs 44 respectively,
and to retain the cup shaped enclosure 20 and housing 26 in
assembled relation. The lugs 44 have sloped camming faces by which
they can be slid past the lip of the housing 26 and seated in the
recesses 46 as the enclosure 20 and housing 26 are telescoped into
one another, compressing the O-ring 42 as in FIG. 1.
The terminal block 30 has an elongate axially-extending central
projection or support 48, and three electrical terminals 50, 52 and
54 in the form of male terminal prongs having anchorage strips or
bases are molded in place at the time the block 30 is formed. The
terminals 50, 52 and 54 are elongate, and with the probe housing 26
assembled to the cup shaped enclosure 20, the anchorage strips
having the terminals 50, 52 and 54 and the projection 48 extend a
substantial distance into the enclosure 20 toward the transverse
end wall 24 thereof.
Referring again to FIGS. 1 and 2, the enclosure 20 has two external
annular grooves 56 which receive sealing O-rings 60 as shown. The
O-rings 60 sealingly engage the inner surface of the fitting 12,
FIG. 5, to prevent liquid in the radiator or vessel 11 from leaking
out past the enclosure 20. Four positioning ribs 62 are provided on
the outer surface of the enclosure 20, having tapered lead-in edge
portions 64.
The enclosure 20 has integrally formed spring retainer fingers 66
with undercuts, which hold the assembled enclosure 20 and housing
26 in position on a mounting flange (not shown) of the fitting
12.
Disposed on opposite sides of the central projection 48 of the
terminal block are support ribs 68, at the ends of which is mounted
a printed circuit board 72. The terminals 50, 52 and 54 extend into
holes in the printed circuit board and are soldered thereto.
There are provided on the printed circuit board 72, a light source
such as a light emitting diode 74, preferably having an integral
condensing lens, and a light sensor means, preferably a
phototransistor 76, also shown with an integral condensing lens.
The two ribs 68 and the terminals 50, 52 and 54 support the printed
circuit board 72 as shown in FIGS. 1, 2 and 5, with the light
emitting diode 74 and phototransistor 76 being disposed adjacent to
and facing the transverse end wall 24 of the enclosure 20.
The end wall 24 comprises a lens formation 78 which operates to
reflect either more or less light from the light emitting diode 74
to the phototransistor 76, according to whether or not the outer
surface of the lens 78 is in contact with either air or liquid.
When the outer surface of the lens 78 is immersed in air,
sufficient light from the light emitting diode 74 is reflected
internally of the lens 78 and strikes the phototransistor 76,
causing it to conduct and, through suitable alarm circuitry shown
in block diagram form in FIG. 8, be employed to indicate a low
level of liquid.
On the other hand, when the outer surface of the lens 78 is
immersed in liquid, the quantity of light reflected by the lens 78
to the phototransistor 76 is normally not sufficient to render the
phototransistor conducting.
However, in the use of modules having a substantially conical lens
configuration of the types illustrated in U.S. Pat. Nos. 4,840,137
and 4,859,987 noted above, it has been found that when such modules
were used directly in the particular radiator installation
corresponding to FIG. 5 of the present application, an erroneous
low liquid level indication might often be shown. This was true
especially where the radiator 11 had its internal core wall 18
somewhat shiny, as with some degree of light-reflecting properties,
and where a generally translucent anti-freeze liquid 98 was being
employed in the radiator, such as ethylene glycol anti-freeze
solution. As presently understood the erroneous readings occurred
because stray light that originated at the light emitting diode and
passed outward through the lens and anti-freeze solution, struck
the wall 18 and was reflected therefrom. Some of this reflected
"stray" light re-entered the lens 78 and struck the
phototransistor. The resultant conduction of the phototransistor
corresponded to an erroneous low liquid level indication, and this
false reading thus presented a problem with the prior patented
constructions.
In accordance with the present invention there is provided on the
outer surface of the lens 78, a prism structure which has the
desired effect of dispersing or altering light which could be
transmitted through it, thereby to reduce the undesirable effect of
stray light reflections off of surfaces (such as the wall 18)
within the radiator 11; this reduces the intensity of the reflected
light which might reach the phototransistor 76.
In the embodiment of FIGS. 1-6, the prism structure takes the form
of a plurality of substantially parallel ribs or ridges 80
separated by grooves 82 in the outer surface of the lens 78, the
ribs 80 at their ends being a part of an original conical surface
of the lens. FIGS. 5 and 6 show the construction in more detail. In
particular, the periphery 83 of the lens is substantially conical;
a series of three grooves 82 extends transversely of the axis of
the enclosure 20. The angle between the walls of the grooves has
been found to be of importance, lying preferably between 70.degree.
and 90.degree., with an optimal figure of 84.degree. having been
determined. This angle is indicated by the letter A in FIG. 5. The
angle which the surface 83 makes with respect to the axis of the
enclosure 20 is optionally 45.degree.. This angle is indicated by
the letter B in FIG. 5.
A center recess or blind hole 85 is preferably incorporated in the
transverse end wall 24, to facilitate molding. The material out of
which the cup shaped enclosure 20 and lens 78 is made can be
polyethersulfone. The material of the module housing 26 is
preferably a polyester-type plastic containing 15% glass.
Also in accordance with the invention and referring to FIG. 8, the
light emitting diode 74 is excited with a high-intensity, short
duration electrical pulse having an amplitude which exceeds the
steady state current rating of the device, but which is present for
a sufficiently short time so as not to damage the device. The
intensity of the resultant light burst emitted by the light
emitting diode 74 is significantly greater than that obtainable
with steady state excitation thereof, and as presently understood
is considered to contribute significantly to the relatively high
sensitivity of the probe to even relatively minute changes in the
quantity of light received by the phototransistor 76. In FIG. 8,
the pulse is provided by a pulse generator 86 connected to the
input of the light emitting diode 74. The vehicle's battery is
designated 88, and the ignition switch designated 90'. The output
of the phototransistor 76 is fed to an amplifier 92', which in turn
drives an alarm or warning light 94 preferably located on the
vehicle dashboard (not shown).
Also, in FIG. 8 the terminals 50, 52 and 54 are shown, and an
electrical connector 96 provided to mate therewith, and to carry
the proper signals between the light emitting diode 74,
phototransistor 76, and the circuitry comprising the amplifier and
pulse generator. The terminal 52 is seen to be common to both the
light emitting diode 74 and the phototransistor 76. Details of
specific electrical connections between the phototransistor 76, the
amplifier 92' and alarm 94 of FIG. 8 are discussed in U.S. Pat. No.
4,859,987 identified above, and thus need not be repeated.
The light emitting diode 74 may, for example, be a GaAlAs (gallium
aluminum arsenide) infrared light emitting diode of the type
manufactured by Optek Technology, Inc. The phototransistor 76 may
be, for example, an all NPN silicon phototransistor of the type
also manufactured by Optek Technology, Inc.
As presently understood, light rays which have been emitted by the
light emitting diode 74 and which pass outwardly through the
forward end of the lens 78, are scattered to some extent as they
enter the liquid in the radiator 11, i. e. the ethylene glycol 98,
for example, (in the case of the outer surface of the lens 78 being
submerged). Reflection of certain rays from the core wall surface
18, some of which would impinge on the lens 78 adjacent the
phototransistor 76 are similarly scattered or diffused a second
time, to the extent that the intensity of these "scattered,
reflected" rays or beams, when received by the phototransistor 76
is attenuated and insufficient to render it conductive. Stated
another way, the prismatic configuration on the exterior of the
lens 78 disperses light reflected from the wall 18, preventing such
reflected light from activating the phototransistor 76.
As a consequence, with the discovery made by the inventors, the
phototransistor 76 does not substantially respond or go into
conduction, when struck by stray light rays which are externally
reflected off the core surface 18 and when the outer surface of the
lens 78 is immersed in liquid. However, the phototransistor 76 does
receive sufficient light to conduct when struck by rays that are
internally reflected in the lens 78 when the outer surface of the
lens is not immersed in liquid, corresponding to a low liquid
condition.
Thus, by the invention the disclosed combination of a light
emitting diode 74 excited by a short-duration, high-intensity
electrical pulse, a phototransistor 76 and lens 78 having a prism
formation 80, 82 enables the module to discriminate between: 1)
light being mostly reflected within the lens 78, as a consequence
of the outer surface of the lens 78 not being immersed; and 2)
stray light which is reflected off the core wall 18 and through a
translucent liquid 98 when such liquid is above the level of the
lens 78, i. e. the outer surface of the lens is submerged in the
translucent liquid. The light reflected from the wall 18 is
considered to be the stray light, and the ability of the module to
differentiate between the internally reflected light within the
lens 78 and the reflected light from the core wall 18 is as
presently understood, largely responsible for the success of the
probe in providing true readings of liquid level in the radiator
11, without regard to the specific translucency of the liquid
98.
While the disclosed embodiments have been described as being
applicable for use in an automobile radiator to monitor the level
of coolant such as ethylene glycol, it can be readily understood
that the device is applicable to other types of vessels and with
other liquids of a translucent, or semi-translucent nature.
In FIG. 5 where the components are shown greatly enlarged, the
distance between the jacket wall 14 of the reservoir area and the
core support wall 18 can vary from 0.158 inch, down to 0.095 inch,
the latter being represented by the wall 18' shown in dotted
outline in FIG. 5. The above figures could be used with a lens
having as a diameter, a figure of 0.22 inch, for example.
Yet another embodiment of the invention is shown in FIG. 7, wherein
in place of the lens configuration of FIGS. 1-6, a modified lens
78a is illustrated, having a peripheral conical portion 83', and a
series of pyramid-like prisms 85' disposed therebetween, side by
side. The central or inner surface of the pyramids is generated by
three grooves extending transversely of the cone 83' and an
additional three grooves perpendicular to the first three grooves,
also extending transversely of the cone axis. In such case, the
radially outermost surfaces of the pyramids are constituted as
sections of a conical surface having the same curvature as that of
the cone 83'. The surfaces of the innermost pyramids are mostly
planar, being constituted as plane sections which lie within the
planar walls of the transverse grooves.
The lens configuration illustrated in FIG. 7 has been found to be
adaptable to the module of FIGS. 1-6, and to provide a similar
desired "light scattering" characteristic which enables the probe
to discriminate between reflected light within the lens itself, and
stray reflected light. In particular, the stray light is that which
has passed through the translucent liquid in which the outer
surface of the lens is immersed, and has been reflected off the
core surface 18 and re-enters the lens 78a, to strike the
phototransistor 76.
Still another embodiment of the invention is shown in FIGS. 9 and
10, which illustrate a further modified lens configuration 78b on a
cup shaped enclosure 20b, the lens configuration comprising a
substantially conical peripheral outer ring portion 90, and a
series of concentric, circular ridges 92 separated from one another
by grooves. In this construction, an advantageous symmetry is
realizeable, and there is thus eliminated any reliance on the
relative positioning between the light emitting diode 74,
phototransistor 76, and grooves such as those indicated between the
ribs 80 in FIGS. 5 and 6. Again, with the construction of FIGS. 9
and 10, the lens configuration provides the desired "light
scattering" characteristics which enable the probe to discriminate
or differentiate between: 1) reflected light within the lens 78b
itself; and 2) stray reflected light that has exited the lens 78b,
passed through translucent liquid 98 in which the outer surface of
the lens 78b is immersed and been reflected off the wall 18 to
re-enter the lens 78b and strike the phototransistor 76.
It has been determined that an optimal angle for the surface 90
with respect to the axis of the lens 78b is 45.degree.. An optimal
angle between the walls of the grooves between the ribs 92 is
typically 84.degree., with a radial spacing between the ribs of
0.017 inch, and a groove depth of 0.008-0.011 inch, measured from
the plane containing the peaks of the ribs. FIG. 9 is presented
roughly at a scale of 10:1, with respect to an actual lens
construction.
In practice, the conical faces of the circular grooves between the
ribs 92 need not be polished smooth. A matte finish has been found
to provide acceptable results, possibly for the reason that the
light scattering or dispersing effect of the ribs is somewhat
enhanced with such a non-smooth finish.
From the above it can be seen that we have provided a novel and
improved liquid level monitor which effectively eliminates the
undesired effects of stray light reflections from internal surfaces
in the vessel, which reflections were found to seriously adversely
affect the operability of the patented devices.
The solution to the problem involving stray reflected light, as
discovered by applicants, is seen to be simple and straightforward,
and capable of implementation without the need for complex physical
barrier structures in the tank, or alternately extensive electrical
processing of the phototransistor-derived signals in order to
accomplish the desired discrimination function.
As presently understood, the monitor is adaptable to virtually any
tank structure and capable of operation with a variety of liquids,
whether translucent, opaque, or having light transmitting
characteristics falling somewhere between these limits.
The disclosed solution as set forth by applicants is thus seen to
represent a distinct advance and improvement in the field of liquid
level indicators.
Variations and modifications are possible without departing from
the spirit of the invention.
Each and every one of the appended claims defines an aspect of the
invention which is separate and distinct from all others, and
accordingly it is intended that each claim be treated in this
manner when examined in the light of the prior art devices in any
determination of novelty or validity.
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